In the statement, Flake said he appreciated the attempt to reform the tax code but said he was worried about its potential effect on the national debt.

“I remain concerned over how the current tax reform proposals will grow the already staggering national debt by opting for short-term fixes while ignoring long-term problems for taxpayers and the economy,” Flake’s statement said. “We must achieve real tax reform crafted in a fiscally responsible manner.”

Flake’s concerns are indicative of a possible tripping point for the Senate bill, the Tax Cuts and Jobs Act (TCJA). Other GOP senators, such as Bob Corker, have also expressed concern with the potential impact to the deficit and debt.

While the bill can pass on a party-line vote and without being blocked by a Democratic filibuster, Republicans only hold 52 seats in the Senate. Leaders can only afford two defections for the bill to pass.